1. Field of the Invention
The invention relates to a method of identifying objects provided with a code field containing a dot code, which code field can be presented in different positions to a pick-up device. The identification can be an individual amount of information for the relevant object or an amount of information for a group of objects. In a manufacturing process such an identification can be advantageous with a view to inventory control, or for associating an object with test results applicable to it. The identification may also indicate a test result relating to an earlier manufacturing step.
2. Description of the Prior Art
The use of a so-called bar code is now general practice. This code works very reliably, but takes up a large area on the object. A dot code is disclosed in the United States patent No. 4,263,504. In themselves, dots take up less space than bars. The known dot code is used for coding alphanumeric characters, a cyclically transposable codeword being used for each character. Each character fills a column of the code field wherein the relevant codeword is applied twice in succession. For this reason the detection is largely independent of the position of the pick-up window along the column of characters.
It is evident that the known art still requires a large area for the identification. As an initial improvement of the known method a code field is therefore taken with dimensions that are of the same order of magnitude in both coordinate directions. In particular the code field then has a shape that possesses a certain degree of rotational symmetry, for example twofold (rectangle), threefold, fourfold or sixfold. (Other multiples are also possible.) In this case, then, the code field has to contain orientation information. The known code, however, is not proof against multilations: a wrongly read dot also implies an erroneous identification and possibly therefore a wrong orientation.